Random Number generator printing a pattern

Question

I am trying to create a Dice Roll game where the user can roll up to 6 dice at a time. I am attempting to accomplish this by integrating pointers into my code. I am getting an output, with the desired amount of rolls as given by the user, but the output is incorrect. It is printing a pattern instead of printing random numbers. Any help is appreciated.

How many dice would you like to roll?
user input: 4
output: 3 0 3 0

How many dice would you like to roll?
user input: 5
output: 4 0 4 0 4

#include <stdio.h>
#include <stdlib.h>


void tossDie(int []);


int main() {

int diceArray[6] = { 0 };
int num = 0;
int x;


do {
    printf("\nHow many dice would you like to roll? Please enter here: ");
    scanf_s("%d", &num);//user enters amount of dice they want to roll)

    if (num < 1 || num > 6) {
        printf("\n\nPlease enter a number between 1 and 6.\n\n");
    }
} while (num < 1 || num > 6);


tossDie(diceArray);


//print dice roll numbers
for (x = 0; x < num; x++) {
    printf("%d ", diceArray[x]);
  }

  return 0;
}

 void tossDie(int numbers[]){

  int randomNum;
  int x;

  srand(time(NULL));
  randomNum = (rand() % 6) + 1;  //random # between 1 - 6


  for (x = 0; x < 6; x++){
      numbers[x] += randomNum;
      x++;
    }
  };

You have `x++` twice. And you are only getting a single `randomNum` rather than a random value for each loop iteration so of course every resulting number will be the same. — kaylum, Oct 20 '21 at 19:31
`srand` should be called exactly once, when the program starts. See https://stackoverflow.com/questions/7343833/srand-why-call-it-only-once for more info. — user3386109, Oct 20 '21 at 19:32
Also, srand() must be run *exactly once*, at the start of the program, not inside a function that's called inside a loop, as here (move it into main()). — Lee Daniel Crocker, Oct 20 '21 at 19:32

chux - Reinstate Monica · Accepted Answer · 2021-10-20T19:48:03.793

Move srand(time(NULL)); to main(). Only needed once.
Only call x++ only per loop, not twice, to assigned all 6 elements of the array.
Move randomNum = (rand() % 6) + 1; to inside for loop to get different values.
Check return value of scanf_s("%d", &num); against 1, before using num.

Tip: Use an auto-formatter to save time and improve code presentation.

Design: I'd expect tossDie(int numbers[]) to also receive a num to indicate numbers[] width.

score 2 · Answer 2 · answered Oct 20 '21 at 19:47

Before I answer, please note that I don't program in C, so there may be some language-specific things that I am missing.

In your tossDie() function, you set the value of randomNum once, but don't reassign it after that. Therefore, your output should return the same number for all values in the array, like such:

Input: 5

Output: 3 3 3 3 3

To fix that, you should put the variable declaration in the for loop (if you want to use a variable at all).

Additionally, you initialise the random variable every time you run the method. Instead, you should declare it once, in the main method.

Also, there's a little issue in this block of code:

for (x = 0; x < 6; x++){
  numbers[x] += randomNum;
  x++;
 }
};

You increase x twice in here: both in the first line and the third line. Instead, you should delete the x++ in the third line and have just the x++ in the first line.

Let me know if you have further questions or if there are still problems.

Random Number generator printing a pattern

2 Answers2